Assessing Performance Goals and Operational Limitations across Capacitive Deionization Technologies

Membrane capacitive deionization (MCDI) is a modification of capacitive deionization (CDI) using ion-exchange membranes (IEM) in front of the electrodes. Electrode properties, especially the specific surface area, are known to be strongly related with desalination performance in CDI, but the effects of other properties in MCDI are not fully understood. The objective of this study was to investigate the effect of hydrophilicity in activated carbon electrodes on desalination performance in MCDI. Two types of activated carbon (P60 and YS-2) whose specific surface areas were similar were used as electrode materials, but they had different hydrophilicity (i.e., P60 was originally hydrophobic and YS-2 was relatively hydrophilic due to its nitrogen-containing surface chemistry). These hydrophilic electrodes (either the electrode itself or modified with polydopamine (PDA)) led to an increase in the salt adsorption capacity (SAC) in MCDI because they facilitated the access of both ions and water molecules into the electrode pores. In particular, the SAC of the P60 electrode displayed a large increase to almost reach that of the YS-2 electrode due to the improved hydrophilicity with PDA modification and the insignificant effects of PDA modification on an already hydrophilic YS-2 electrode. Additionally, PDA-modified IEM in MCDI reduced the SAC as a result of the additional insulating PDA layer with little changes in hydrophilicity.

ZiF-8 induced carbon electrodes for selective lithium recovery from aqueous feed water by employing capacitive deionization system

It is known that capacitive deionization (CDI) is not suitable for direct desalination of seawater because of its high salinity (~ 35 g L−1) and the limit in applied potential to avoid water electrolysis and oxidation of chloride ions. It has recently been reported, however, that the potential window can be expanded with the formation of an electrode-electrolyte interphase when using highly concentrated aqueous electrolyte. Studies also have proven that increasing ion concentration can greatly enhance the ion capacity of the electrodes. In addition, ion-exchange membranes (IEMs) can be used to control the electrode performance and allow application of reverse potential for electrodesorption. Here, we present the possibility to directly desalt high-salinity water and seawater through membrane CDI (MCDI). An MCDI cell was symmetrically assembled with anion and cation exchange membranes attached respectively to the anode and cathode. Our results show that the MCDI cell equipped with mesoporous carbon can remove 66.7 mg sodium chloride per gram of carbon, while the CDI cell alone (without membranes) could only remove 8.5 mg g−1 under the same conditions. Similarly, the MCDI cell equipped with carbon aerogel demonstrated a salt removal capacity of 37.3 mg g−1 in comparison with 12.9 mg g−1 of the CDI cell. These results indicate that the MCDI cell, assisted with IEMs and overpotential, can directly desalt high-salinity water regardless of the electrode material. Moreover, IEMs can prevent coion desorption at the beginning of the adsorption stage, as well as counterion adsorption at the beginning of the desorption stage, which can increase energy efficiency. For high-salinity water desalination, electrode regeneration is challenging. By applying a reversed low potential and controlling the desorption time, electrode regeneration can become effective. The presentation will include a review of CDI approaches, motivation for overpotential CDI supported by neutron imaging of electrodes and basic electrochemical experiments, characterization of electrode materials, a discussion of overpotential CDI and MCDI results including energy requirements, and a discussion of remaining challenges for direct desalting of high-salinity water via MCDI.

With the gradually increasing requirement for freshwater, capacitive deionization (CDI) as a burgeoning desalination technique has gained wide attention owing to its merits of easy operation, high desalination efficiency, and environmental friendliness. To enhance the desalination performance of CDI, different CDI architectures are designed, such as membrane CDI, hybrid CDI, and flow-electrode CDI. However, these CDI systems have their own drawbacks, such as the high cost of membranes, capacity limitation of carbon materials and slurry blockage, which severely limit their practical application. Notably, rocking-chair CDI (RCDI) composed of symmetric electrode materials delivers excellent desalination performance because of its special dual chamber structure, which can not only break through the capacity limitations of carbon materials, but also deliver a continuous desalination process. Although RCDI showcases high promise for efficient desalination, few works systematically summarize the advantages and applications of RCDI in the desalination field. This review offers a thorough analysis of RCDI, focusing on its electrode materials, structure designs and desalination applications. Furthermore, the desalination performances of RCDI and other CDI architectures are compared to demonstrate the advantages of RCDI and the prospect of RCDI is elucidated.

Nitrogen-doped nanostructured carbons: A new material horizon for water desalination by capacitive deionization

Capacitive deionization is an emerging electrochemical technology employed in water desalination applications. Multiple water desalination technologies include reverse osmosis, multi-stage flash, humidification-dehumidification, and nanofiltration. Capacitive deionization is appreciably increased the desalination efficiency compared to other technologies while promising energy-efficient and cost-effective operation. In the CDI system, the charged ions are extracted from feedwater by applying an electrical voltage across electrodes, in which the charged ions are attracted to the oppositely charged electrodes. This paper demonstrates the concept of capacitive deionization (CDI), the components of CDI cell, working principal, and performance metrics for the CDI system. Furthermore, the paper reviews the state of technology of the CDI cell and the development of the system since the mid-1960, including the concepts of membrane and flow electrode CDI. Finally, a cost analysis framework of CDI, MCDI, and FCDI is demonstrated based on the Levelized cost of water.

Desalination of brackish water containing oil compound by capacitive deionization process

Intrinsic tradeoff between kinetic and energetic efficiencies in membrane capacitive deionization

Emerging MXene-based electrode materials for efficient capacitive deionization: A comprehensive review

The polymeric conformational effect on capacitive deionization performance of graphene oxide/polypyrrole composite electrode

Treatment of industrial brine using capacitive deionization (CDI) towards zero liquid discharge – challenges and optimization

With the increasing global water shortage issue, the development of water desalination and wastewater recycling technology is particularly urgent. Capacitive deionization (CDI), as an emerging approach for water desalination and ion separation, has received extensive attention due to its high ion selectivity, high water recovery, and low energy consumption. To promote the further application of CDI technology, it is necessary to understand the latest research progress and application prospects. Here, considering electric double layers (EDLs) and two typical models, we conduct an in-depth discussion on the ion adsorption mechanism of CDI technology. Furthermore, we provide a comprehensive overview of recent advances in CDI technology optimization research, including optimization of cell architecture, electrode material design, and operating mode exploration. In addition, we summarize the development of CDI in past decades in novel application fields other than seawater desalination, mainly including ionic pollutant removal, recovery of resource-based substances such as lithium and nutrients, and development of coupling systems between CDI and other technologies. We then highlight the most serious challenges faced in the process of large-scale application of CDI. In the conclusion and outlook section, we focus on summarizing the overall development prospects of CDI technology, and we discuss the points that require special attention in future development.

Capacitive deionization (CDI) is a potential technique for water treatments such as brackish water desalination, seawater desalination, wastewater remediation, and water softening. CDI has more advantages over other desalinating processes: (i) the technique works by the process of electroabsorption, and is even more energy-efficient, as it does not require any high-pressure pumps; (ii) as the module works in 0.8–2.0 V. An ideal electrode for CDI system requires the following characteristics: (i) large surface area; (ii) high porosity (both meso and micropores); (iii) high electrical conductivity; (iv) electrochemical stability; (v) bio-inertness; (vi) fast adsorption-desorption kinetics; (vii) good wetting behavior; (viii) low cost; and (ix) scalability. In Vietnam, coconut shell-derived activated carbon is produced by a calcinated process under nitrogen gas, which exhibits a high surface area (800-1000 m2/g). In this work, we prepared the CDI composite electrode based on coconut shell-derived activated carbon and high conductive carbon like CNTs or carbon black in the pilot scale. CDI systems with a capacity of 1 m3 per day were fabricated and monitored the desalination performance in Mekong Delta.

Zinc oxide nanosheet decorated self-supporting hierarchical porous wood carbon electrode for efficient capacitive deionization defluorination

The literature on capacitive deionization (CDI) of water is discussed. The CDI is a new method of water desalination which consists of pumping water to be deionized between highly disperse carbon electrodes with a certain potential difference applied to these electrodes. The CDI is characterized by the lower expenditure of energy as compared with the other desalination methods. Different modifications of CDI are considered such as membrane capacitive deionization (MCDI), CDI with redox reactions on electrodes, and CDI with flow-through electrodes. The dependence of CDI on the porous structure of electrodes, the size of hydrated ions, the type of carbon used for electrodes, the electric double layer capacitance, the presence of functional groups, the wettability of electrodes, the pH, and other factors is considered. The problems of the production of pure drinking water and also of the degradation of electrodes are discussed. The use of CDI in practice is described.